Digitate Hydroids (Good Or Bad?)

Image Credit: ReefJunkee via Nano-Reef
Image Credit: ReefJunkee via Nano-Reef

Digitate Hydroids (Good Or Bad?)


You may never have heard of these pests before, but they can be a nightmare to remove from your aquarium system. Luckily, Reef Tank Resource has everything you need in case you spot one of these unsightly creatures in your tank, whether it’s in the early days of infestation or months in.

There are plenty of methods you can try to remove the unsightly wormy creatures from your aquarium. From creatures that will help scour the aquarium for the pests to more direct methods of removal, we have plenty of tips and insights into maintaining your aquarium.

Are Digitate Hydroids Good Or Bad?

Digitate hydroids, and other hydroids found in reef aquariums, are known to sting corals and fish. They definitely fall into the “Bad” category.

They are difficult to remove but there are some predators that may consume them. For example the Lynx Nudibranch and the Flameback Angel. Manual removal and dosing hydrogen peroxide may work also.

What are Hydroids in a reef tank?

Hydroids can take two forms in a saltwater tank. The first form is called a medusa where the mouth faces down and is relatively free-floating.  The other form is the colonial hydroids phase which is made up of polyps where the mouth faces upward. Often a hydroid will experience both of these phases in its lifetime.

The different polyps that make up the colony all have different tasks ranging from killing prey to digestion. When the pest is in the polyp phase, it is often attached to rock or coral to get a foothold within the tank. The tentacles that reach out of the polyp can kill, they do pose a risk to coral and fish within your reef tank.

Are Hydroids bad?

That completely depends on the population of your tank and how many digitate hydroids you have in your aquarium. There is evidence to suggest they will definitely pose a threat to several species in your tanks, like SPS corals, Zoanthids, and some species of fish. On top of this, the population can quickly get out of control if the environment supports it.

However, some people have found that their population of hydroids has disappeared after only a day or two. Obviously, their tanks were not adequately supporting the population. On the flip side, many aquarists didn’t know that the squiggly white worm in their tank was a hydroid which resulted in a population boom for the species in several weeks. Once the population starts to get big, it can become more difficult to eradicate it from your aquarium’s system.

What will eat Hydroids?

If you have noticed that you have a hydroid problem, there are several fish and other marine species that might be able to help get rid of your problem.

  • Lynx Nudibranch –  almost exclusively eats hydroids so it might not be a good idea to try to own one permanently since you will be risking the creature’s health after your problem is solved. If you have an aquarist friend, you might be able to borrow one for a few weeks or months to get rid of the pests from your tank. If not, there are plenty of other marine species to choose from.
  • Sea Urchin Salmacis bicolor – Can be a little slow but it will also do a fine job of slurping up the hydroid in your rock over time.
  • Flameback Angelfish – There is the potential this fish will fight the good fight and feed on the invasive pests but there is also a chance it will ignore them and nibble at your corals.
  • Pterolidia Ianthina – This little sea slug is also a big eater of the hydroid.

Will peppermint shrimp eat Hydroids?

Peppermint shrimp are a big help with some pests but are they as helpful with the pesky hydroid? The answer is sometimes. Like any animal that has a wide diet, there is no guarantee that the species will eat the invaders if there are other more appetizing options available.

It also may depend on the type of hydroid that is in your tank. There is recorded evidence that peppermint shrimp will treat aiptasia as their food source but there isn’t much confirmation on other types.

How big do Hydroids get?

It often can depend on the exact species that you are dealing with but at the very most you can expect a colony to reach around 5 inches wide and 1.5 inches tall. That is quite large depending on the size of your tank and will not leave some of your fish and invertebrates many places to run to.

How do Hydroids reproduce?

In the polyp phase of the life cycle, all species will reproduce asexually by using one of their polyp tentacles to split off into more larvae. This is part of the reason why the pest can become so troublesome so quickly. The fact that there doesn’t need to be more than one in your tank for their to begin to be a problem can pose a huge risk to your fish and corals. It makes it so that there is little chance they will go away on their own if they have a food source.

Do hermit crabs eat Hydroids?

There isn’t a lot of evidence to suggest that most hermit crabs will regularly kill a hydroid. In fact, some hermit crabs have been known to wear shells that are covered in hydroid polyps.

Do Hydroids sting?

It depends on the species but some do like the stinging hydroid. The only good thing about this species is that it mostly feeds on plankton but the flip side is that its sting can be a major pain and pose a risk to your fish and corals. The stinging can hurt a lot if you are not careful yourself so if you are trying to remove the pest manually, be sure to wear gloves and take other safety measures to protect yourself.

Manual removal

If the population is low, it might be best to simply remove the pest manually. First, search and find every possible location where the pest might be. Once you have every known location marked, take a pair of tweezers, move towards their post, and remove them at the base of their bodies. Be very careful upon removal to avoid them escaping somewhere else.

Alternatively, you can try sealing the pests inside their homes with epoxy. The epoxy will prevent them from going anywhere and they will starve.

Will peroxide kill Hydroids?

There is a chance you might be able to dose peroxide or directly inject it into the pest to eliminate it from your tank. This works great if you are not dealing with a lot of the pest. The only problem with peroxide is that it can destroy the beneficial bacteria that exist in your water column.

Fenbendazole use against hydroids

One can be a great way to help remove this pest from your rocks and aquarium system is to apply fenbendazole to it. However, the best way to apply this treatment is before the live rocks have even been introduced into your reef tank. You can find this product at some fish retailers but you might find more success at your local tractor supply store, depending on your location. The treatment can be used as a dip to help prevent pests like bristle worms and hydroid from getting into your tank in the first place.

The best thing about this treatment is that it will not have adverse effects on the good bacteria in your tank unlike other treatment methods like peroxide. During treatment, if you are doing it directly in your tank, you will need to turn off filter methods like your protein skimmer, UV sterilization, and make sure your carbon is removed.

You should dose your tank with between 0.1 and 0.2 mL per gallon. You should repeat this every day for at least 3 days to help control the spread. However, if it seems like the spread is no being reduced, you may need to continue for as long as a week.

Fenbendazole is a dewormer that will work to kill other pests in your system too. If you have a lot of these worms in your system, there is a good chance that your water parameters will begin to skew with a spike in ammonia.  After your treatment, you should perform a water change and test the quality of your water. If you noticed a large change, you may need to take additional steps to stabilize the parameters.

Digitate hydroids laser

You can try to use an aiptasia laser to remove the polyp colony from your reef aquarium but there are a few things that you should keep in mind before you begin slicing through your reef aquarium.

The laser is expensive and can do some serious damage to the organisms in your aquarium if you are not careful. You must follow the safety precautions that are listed for the laser carefully to avoid self-injury and proper use. It is a laser that is capable of removing organisms from almost any location after all.

However, some people disagree with their use at all. Like member salty joe from the forum reef2reef who says that “lasers are too dangerous to use for pest control.” However, a laser could work but it can be dangerous. If you notice that your pest has not multiplied too badly yet, you could try to remove it with a laser with proper protection and no kids in the room.

Digitate hydroids dip

If you noticed that there is a polyp on one of the pieces that you just bought, you could try to create a dip to help remove the hydroid from live rocks before you introduce them to your reef aquarium or if you are able, you can take the live rock out and dip it to remove. Depending on the dip method, you may remove beneficial bacteria from the post, so keep that in mind before you just choose whatever you have on hand to treat the location of the pest.

The best thing you can use is fenbendazole to use as a dip as it will remove the pests without killing all the beneficial bacteria in the location. However, if that doesn’t work, you may need to use a peroxide dip.

Final thoughts

Digitate Hydroids can pose a threat to your zoa, fish, and the overall picture of your aquarium. If you notice one of them in your aquarium, it is best to handle the situation immediately rather than putting it off until later. Make sure you search adequately so you don’t accidentally leave one location unresolved. Like any pest, it is much easier to deal with them as soon as possible.

Speaking of dealing with pests, I suggest you check out our article covering the best clean-up crew critters. These little guys can help prevent pest problems before they actually become a problem.

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